Port wine is typically thicker, richer, sweeter, and possesses a higher alcohol content than most other wines. This is caused by the addition of distilled grape spirits to halt fermentation before all the sugar is converted to alcohol. It is commonly served after meals as a dessert wine, or with cheese.
Vintage port is made entirely from grapes of a declared vintage year. Not every year is declared a vintage in the Douro, only those when conditions are favorable to particularly flavorful crops of grapes. The decision to declare a vintage is made by each individual port house, and is based on several factors, most notably the weather and the ability of the marketplace to absorb a new vintage. While it is by far the most renowned type of port, from a volume and revenue standpoint it actually makes up a small percentage of the production of a typical port house. Vintage ports are aged in barrels for a maximum of 2 years before bottling, and often require another 5 to 15 years of aging in the bottle before reaching what is considered proper drinking age. Since they are aged in barrels for only a short time, they retain their dark ruby color and fresh fruit flavors. Particularly fine vintage ports can continue to gain complexity and drink wonderfully for decades after they were bottled, and therefore can be particularly sought after and expensive wines.
"Port" produced outside of Portugal may be labeled with a vintage date, but is not real Vintage Porto and likely is meant for immediate consumption rather than extended aging.
Ruby and tawny Port may contain wine from several vintages. Vintage, ruby, and LBV ports are fermented in wood and aged in glass, which preserves the wine's red color.
LBV (Late-Bottled Vintage) port is intended to provide some of the experience of drinking a vintage port but without the decade-long wait. In contrast to vintage port's short time in barrel, LBV port is aged for several years in barrel to mature it more quickly. Typically ready to drink when released, LBV ports are the product of a single year's harvest and tend to be smoother and lighter-bodied than a vintage port. The confusingly named Vintage character port is similar to LBV port.
Tawny port is aged in wooden barrels, exposing it to gradual oxidation and evaporation, causing its color to mellow to a golden-brown after roughly ten years "in wood." Often they have pronounced "nutty" flavors. Most tawny port is a blend of several vintages, with the average years "in wood" stated on the label: 10, 15, 20, and 30 years are common. Tawny ports from a single vintage are called Colheitas. Tawny and Colheita ports are always ready to drink when released and do not typically benefit from aging in bottle, although they will not degrade either. Because is has already been exposed to oxygen, an open bottle of tawny resists oxidation the longest of all ports.
"Tawny" port produced outside Portugal is rarely aged long enough to develop a natural tawny color. Instead, it is the result of blending "ruby" and "white" ports, or possibly the addition of caramel coloring.
White port is made from white grapes, and generally served as a chilled aperitif. Ruby port is aged minimally, and is mostly used for cooking or blended into cocktails.